484
Screw Cutting*
Ex-ample 42.—Arrange the gearing of a single purchase crab so
that 6olbs. on a 15" handle may raise half a ton from a barrel 10"
dia., neglecting friction. (Eng. Ex., 1891.)
Mech. adv.
W follower
_ . x
handle
driver barrel rad.
1120
~6o~
1 1 20 follower
_ ___
60
1 5
_ _ ^
driver 5
follower __ 6*22
driver ~~~ I
So the pitch line diameters may be 6" and 37'32" for pinion and
wheel respectively, as in Fig. 442. (Seep. 955.)
Example 43.—A shaft A has a spur wheel of 120 teeth, which drives
a pinion B with n teeth. On shaft B is a wheel of 132 teeth driving
a pinion C of 10 teeth. Lastly, on shaft C is a wheel of 48 teeth
driving a pinion D of 8 teeth. A turns at 2 revs, per m. Find speed
of D. (Eng. Ex., 1885.)
The wheels are shewn in Fig. 443.
vel. D __ followers = 120>jx * 32^*^48 __ 864
vel. A ~" ""drivers 11 x 10 x 8 I
/. D makes 864 x 2 = 1728 revs, per m.
Example 44.—Two men at a crab exert 60 Ibs. each on a 16"
handle. The pinion has 12 teeth, the wheel 72 teeth, and the chain
barrel is 12" diameter. Find the load raised, neglecting friction.
(Eng. Ex., 1888.)
followers x handle = 72 x 16 _ 16
i
W
Mech. adv. —
W :
drivers x barrel rod.
16 x P = 16 x 120 =
12x6
1920 Ibs.
. 955.)
Example 45.—In a Weston block the diameter of the large sheave
i s 10", and that of the smaller 9". Find the load raised by a pull of
50 Ibs., neglecting friction.
W 2 A 2 x 10 20
Mech. adv. -fr — 7—u == —;— ^ —
JT _rL — JD I I
/. W « P x 20 = 1000 Ibs.
(See Appendix 7K, /. 954, without fail.}
Change Wheels in Screw-cutting.—-General principles
-re explained at pp. 147 and 212, it being shewn that: